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Package {snapr}

Title: Convenient Snapshot Testing Functions for Packages
Version: 0.1.0
Description: Provides convenient snapshot testing functions for packages, including expect_snapshot_data() for data.frames and expect_snapshot_object() for any R object.
License: MIT + file LICENSE
Language: en-US
Encoding: UTF-8
URL: https://github.com/d-morrison/snapr, https://d-morrison.github.io/snapr/
BugReports: https://github.com/d-morrison/snapr/issues
Depends: R (≥ 4.1.0)
Imports: dplyr, jsonlite, readr, testthat, tidyselect, tools, waldo
Suggests: altdoc, bslib, knitr, quarto, rmarkdown, spelling, withr
VignetteBuilder: knitr, quarto
Config/testthat/edition: 3
Config/Needs/website: quarto
Config/roxygen2/version: 8.0.0
NeedsCompilation: no
Packaged: 2026-05-18 22:19:34 UTC; ezramorrison
Author: Douglas Ezra Morrison [aut, cre]
Maintainer: Douglas Ezra Morrison <demorrison@ucdavis.edu>
Repository: CRAN
Date/Publication: 2026-05-22 20:20:02 UTC

snapr: Convenient Snapshot Testing Functions for Packages

Description

logo

Provides convenient snapshot testing functions for packages, including expect_snapshot_data() for data.frames and expect_snapshot_object() for any R object.

Author(s)

Maintainer: Douglas Ezra Morrison demorrison@ucdavis.edu

Authors:

See Also

Useful links:

Compare RDS files using waldo for better snapshot review

Description

This comparison function loads RDS files and compares the deserialized R objects rather than raw bytes. This enables better visualization in snapshot_review() by comparing the actual object structure rather than binary serialization.

For meaningful diffs in testthat's snapshot_review(), this function compares the R objects after deserialization using waldo::compare().

Usage

compare_file_object(old, new, print = FALSE, ...)

Arguments

old

Path to the old (reference) RDS file

new

Path to the new RDS file to compare

print

logical whether to print waldo::compare output to R console; can become very long for complex objects like lms

...

Arguments passed on to waldo::compare

x,y

Objects to compare. x is treated as the reference object so messages describe how y is different to x.

x_arg,y_arg

Name of x and y arguments, used when generated paths to internal components. These default to "old" and "new" since it's most natural to supply the previous value then the new value.

tolerance

If non-NULL, used as threshold for ignoring small floating point difference when comparing numeric vectors. Using any non-NULL value will cause integer and double vectors to be compared based on their values, not their types, and will ignore the difference between NaN and NA_real_.

It uses the same algorithm as all.equal(), i.e., first we generate x_diff and y_diff by subsetting x and y to look only locations with differences. Then we check that mean(abs(x_diff - y_diff)) / mean(abs(y_diff)) (or just mean(abs(x_diff - y_diff)) if y_diff is small) is less than tolerance.

max_diffs

Control the maximum number of differences shown. The default shows 10 differences when run interactively and all differences when run in CI. Set max_diffs = Inf to see all differences.

ignore_srcref

Ignore differences in function srcrefs? TRUE by default since the srcref does not change the behaviour of a function, only its printed representation.

ignore_attr

Ignore differences in specified attributes? Supply a character vector to ignore differences in named attributes. By default the "waldo_opts" attribute is listed in ignore_attr so that changes to it are not reported; if you customize ignore_attr, you will probably want to do this yourself.

For backward compatibility with all.equal(), you can also use TRUE, to all ignore differences in all attributes. This is not generally recommended as it is a blunt tool that will ignore many important functional differences.

ignore_encoding

Ignore string encoding? TRUE by default, because this is R's default behaviour. Use FALSE when specifically concerned with the encoding, not just the value of the string.

ignore_function_env,ignore_formula_env

Ignore the environments of functions and formulas, respectively? These are provided primarily for backward compatibility with all.equal() which always ignores these environments.

list_as_map

Compare lists as if they are mappings between names and values. Concretely, this drops NULLs in both objects and sorts named components.

quote_strings

Should strings be surrounded by quotes? If FALSE, only side-by-side and line-by-line comparisons will be used, and there's no way to distinguish between NA and "NA".

Value

logical TRUE if objects are identical, FALSE otherwise

Examples

old_obj <- list(a = 1, b = 2)
new_obj <- list(a = 1, b = 3)
old_path <- tempfile(fileext = ".rds")
new_path <- tempfile(fileext = ".rds")
saveRDS(old_obj, old_path)
saveRDS(new_obj, new_path)
compare_file_object(old_path, new_path)

Get darwin snapshot variant for macOS

Description

Returns "darwin" for macOS, NULL for other platforms (Linux/Windows).

Usage

darwin_variant()

Details

This is a specialized variant function for cases where only macOS produces different results while Linux and Windows are identical. Use this instead of system_os() when:

Common use cases:

Value

"darwin" on macOS, NULL on other platforms

Examples

darwin_variant()

Snapshot testing for data.frames

Description

copied from https://github.com/bcgov/ssdtools with permission (https://github.com/bcgov/ssdtools/issues/379)

Usage

expect_snapshot_data(x, name, digits = 6, ...)

Arguments

x

a data.frame to snapshot

name

character snapshot name

digits

integer passed to signif() for numeric variables

...

Arguments passed on to testthat::expect_snapshot_file

binary

[Deprecated] Please use the compare argument instead.

cran

Should these expectations be verified on CRAN? By default, they are not, because snapshot tests tend to be fragile because they often rely on minor details of dependencies.

transform

Optionally, a function to scrub sensitive or stochastic text from the output. Should take a character vector of lines as input and return a modified character vector as output.

variant

If not-NULL, results will be saved in ⁠_snaps/{variant}/{test}/{name}⁠. This allows you to create different snapshots for different scenarios, like different operating systems or different R versions.

Note that there's no way to declare all possible variants up front which means that as soon as you start using variants, you are responsible for deleting snapshot variants that are no longer used. (testthat will still delete all variants if you delete the test.)

old,new

Paths to old and new snapshot files.

Value

NULL (from testthat::expect_snapshot_file())

Examples


# expect_snapshot_data() must be called inside a test_that() block with
# testthat 3rd edition active. Outside a test suite, the snapshot is
# skipped because there is no reference file to compare against.
withr::with_tempdir({
  testthat::test_that("iris snapshot", {
    testthat::local_edition(3)
    expect_snapshot_data(iris, name = "iris")
  })
})

Snapshot testing for R objects

Description

A flexible wrapper around testthat::expect_snapshot_file() that allows snapshotting any R object, not just data.frames. This function provides a convenient interface for snapshot testing with sensible defaults for serialization.

When using RDS format (the default), snapshots are compared using waldo::compare() which provides rich, visual diffs in testthat::snapshot_review(). This makes it much easier to review changes to complex R objects.

Usage

expect_snapshot_object(
  x,
  name,
  writer = save_rds,
  print = FALSE,
  tolerance = NULL,
  ...
)

Arguments

x

An R object to snapshot. Can be any R object including lists, models, data.frames, vectors, etc.

name

character snapshot name (file extension added automatically)

writer

function Function to write the object to a file. Default is save_rds(). Other options include save_json(), save_deparse(), save_csv(). Custom writer functions should accept x and return a file path.

print

logical whether to print waldo::compare output to R console; can become very long for complex objects like lms

tolerance

If non-NULL, used as threshold for ignoring small floating point differences when comparing numeric vectors. Only applies when writer produces an RDS file (the default); silently ignored for text-based formats (JSON, CSV, deparse, etc.). See waldo::compare() for full details.

...

Arguments passed on to testthat::expect_snapshot_file

binary

[Deprecated] Please use the compare argument instead.

cran

Should these expectations be verified on CRAN? By default, they are not, because snapshot tests tend to be fragile because they often rely on minor details of dependencies.

transform

Optionally, a function to scrub sensitive or stochastic text from the output. Should take a character vector of lines as input and return a modified character vector as output.

variant

If not-NULL, results will be saved in ⁠_snaps/{variant}/{test}/{name}⁠. This allows you to create different snapshots for different scenarios, like different operating systems or different R versions.

Note that there's no way to declare all possible variants up front which means that as soon as you start using variants, you are responsible for deleting snapshot variants that are no longer used. (testthat will still delete all variants if you delete the test.)

old,new

Paths to old and new snapshot files.

Details

When using RDS format (the default), snapshots can vary across R versions and platforms even with fixed serialization versions. Consider using variant = platform_variant() for RDS snapshots to handle these differences, or use text-based formats like JSON or deparse for more stable snapshots across platforms and versions.

The RDS comparison uses waldo::compare() internally, which provides rich visual diffs in testthat::snapshot_review(). This is particularly useful for complex objects like models, nested lists, or data structures where byte-level comparison would be difficult to interpret.

Value

NULL (from testthat::expect_snapshot_file())

Examples


# expect_snapshot_object() must be called inside a test_that() block with
# testthat 3rd edition active. Outside a test suite, the snapshot is
# skipped because there is no reference file to compare against.
withr::with_tempdir({
  testthat::test_that("snapshot examples", {
    testthat::local_edition(3)

    # Snapshot a list (RDS format with platform/version variant)
    expect_snapshot_object(
      list(a = 1, b = 2), name = "config", variant = platform_variant()
    )

    # Snapshot a model
    model <- lm(mpg ~ wt, data = mtcars)
    expect_snapshot_object(
      model, name = "model", variant = platform_variant()
    )

    # Snapshot with JSON format (for human-readable diffs)
    # Text formats don't need variants
    expect_snapshot_object(iris[1:5, ], name = "iris", writer = save_json)

    # Snapshot with deparse format
    expect_snapshot_object(
      list(x = 1:5), name = "simple_list", writer = save_deparse
    )
  })
})

Get platform variant including OS and R version

Description

Returns a variant string combining OS and R major.minor version. This is useful for RDS snapshots that vary by both platform and R version.

Usage

platform_variant()

Details

RDS files can produce different binary output across R versions even when using the same serialization version. This function creates variant strings like "linux-4.4", "darwin-4.5", "windows-4.4" to handle these differences.

Use this function with testthat::expect_snapshot_file() when testing RDS files or other formats that vary by both OS and R version.

Value

A character string like "linux-4.4", "darwin-4.5", or "windows-4.4"

Examples

platform_variant()

Save a data.frame to a CSV file

Description

Save a data.frame to a CSV file

Usage

save_csv(x)

Arguments

x

A data.frame to save

Value

character Path to the temporary CSV file

Save an R object to a text file using deparse

Description

Save an R object to a text file using deparse

Usage

save_deparse(x)

Arguments

x

An R object to save

Value

character Path to the temporary text file

Save an R object to a JSON file

Description

Save an R object to a JSON file

Usage

save_json(x)

Arguments

x

An R object to save

Value

character Path to the temporary JSON file

Save an R object to an RDS file

Description

Save an R object to an RDS file

Usage

save_rds(x)

Arguments

x

An R object to save

Value

character Path to the temporary RDS file

Get the current operating system

Description

Returns the name of the current operating system in lowercase. This is a simple wrapper around Sys.info()[["sysname"]].

Usage

system_os()

Details

This function is used with testthat's variant parameter in testthat::expect_snapshot_file() to create OS-specific snapshots when file formats produce different output across platforms.

Common use cases:

Value

A character string: "linux", "darwin" (macOS), or "windows"

Examples

system_os()

These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.